how to reduce image filesize

Depends on what the original is, what you want to use it for, and how much degradation in image quality you can accept.

If the original is a bitmap, you can compress it with ZIP pretty effectively, and loose no quality. Or you can convert it to a lossless compression image type such as PNG and again lose not quality.

If the original is a lossy format such as JPG, then anything you do with it will almost certainly not reduce size, unless the quality is also reduced - even reading a JPG and saving it again will lose you image quality to a greater or lesser extent.

If image quality if not that important, then TIF, JPG and GIF formats all use compression and can dramatically shrink the file size - but they do this by "throwing away" information that the eye can't really see, and this can have dramatic effects if you are going to use the image for anything that needs high resolution, such as graphics design or print production.

There is no "magic bullet" to shrinking anything - if there was, we'd just use it a dozen times, and send a 1K file for every movie! :laugh: